Centrifugal brakes are useful in numerous applications where it is necessary to resist the further acceleration of a rotating object. For various reasons, the speed at which a given device moves must be limited and if the device rotates or includes rotating parts, a centrifugal brake may often be used to take advantage of the centrifugal force generated by the rotating component. As the rotation velocity reaches a given level, the centrifugal brake engages to limit the rotational velocity and thus the speed of the moving device.
A typical situation where centrifugal brakes are helpful involves controlling the spring return rate of a rotary electric actuator. Such actuators are used in a variety of situations for controlling the position of devices such as valves, mechanical dampers, and the like, as employed in process control systems. For example, process control systems frequently use valves which may be adjusted to control the flow of fluids within a conductor system such as a pipeline. Other types of fluid flow control devices, often encountered in process control systems, include dampers which may be actuated for modulating the flow of gases.
Process control systems which use these actuators include heating, ventilating, and air conditioning (HVAC) systems that usually employ a plurality of air handling units comprising interconnected duct work associated with mechanical dampers. The duct work and dampers cooperate for controlling the flow of outside ambient air into a conditioned space, for controlling the flow of air from the space to the ambient, and for controlling air flow between cool and warm air ducts.
In the above-mentioned actuator systems, a power transmission is typically connected between a damper and an electric motor. The motor provides the power to turn the transmission and thus actuate the damper, valve, etc. Often, damper movement must be carefully controlled by an electronic control system so that the damper is appropriately positioned for the desired air flow. However, in the event of a power failure, the damper is usually returned to a fail safe position, such as completely closed or completely open. Spring returns are typically connected to the power transmission to return the actuator to the desired fail safe position.
In many applications, the return spring must be sufficiently strong to hold the actuator at the desired fail safe position with substantial force. For instance, it may be necessary to hold a building's air flow dampers in a closed position with substantial force to promote safety should there be a fire in the building.
When power to the electric motor is interrupted, the strength of the return spring causes great acceleration of the actuator, its power transmission, and the electric motor towards the fail safe position. This rapid rate of acceleration and high component velocities can cause damage to the actuator, the damper, or their component parts, particularly when the device reaches its fail safe position and abruptly stops.
It would be advantageous to use a centrifugal brake which responds to increasing rotational velocity to restrict further acceleration of the components once the rotational velocity reaches a certain level. In this fashion, the return spring would still quickly move the actuator to its fail safe position, but not at a rate which would cause damage.
The present invention addresses the foregoing drawbacks of systems which include rotational components subject to excess velocity.